Hydrogenation catalyst, its method of preparation and use

ABSTRACT

A method of preparing a hydrogenation catalyst, for example, a phthalate hydrogenation catalyst, comprising contacting a silica support having a median pore size of at least about 10 nm with a silylating agent to form an at least partially coated silica support, calcining said coated silica support to form a treated silica support, and depositing a noble metal, preferably ruthenium, on the treated silica support, and optionally contacting the treated silica support with an optional chelating agent to form the hydrogenation catalyst; a hydrogenation catalyst prepared by that method; and a method of hydrogenating unsaturated hydrocarbons, such as phthalates, in which an unsaturated hydrocarbon is contacted with hydrogen gas in the presence of the hydrogenation catalyst of the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 14/916,727, filed Mar. 4, 2016, now allowed, which is a NationalStage Application of International Application No. PCT/US2014/053675filed Sep. 2, 2014, which claims priorities to U.S. ProvisionalApplication Ser. No. 61/892,561, filed Oct. 18, 2013, and EuropeanApplication No. 13197587.2, filed Dec. 17, 2013, the disclosures of eachare fully incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to hydrogenation catalysts, in particularto methods for the preparation of noble metal catalysts, such asruthenium (Ru) catalysts, for use in the hydrogenation of phthalates.

BACKGROUND

Plasticizers are incorporated into resins to increase their flexibility,workability, and dispensability. Phthalates, especially, the highmolecular weight phthalates (HMWP), are used as plasticizers in PVC.Alternatives to phthalates are desirable due to environmental,legislative and regulatory concerns. In particular, the uses ofphthalates as plasticizers are under severe pressure. Hydrogenation ofphthalates produces 1,2-cyclohexyl dicarboxylates, hereinafter alsoreferred to as cyclohexanoates, which can be also used as plasticizers.

Previous research showed that catalysts consisting of Ru supported onalumina (Al₂O₃) with low surface areas are active for the hydrogenationof phthalate to cyclohexanoates. U.S. Pat. No. 5,936,126 (BASF)discloses the hydrogenation of phthalates to cyclohexyl dicarboxylatesusing catalysts consisting of Ru supported on low surface area aluminaat 80 to 120° C. and under 10-20 MPa (100-200 atmospheres) pressure. US2002/0019559 (BASF) discloses a catalyst for hydrogenation of phthalatescomprising ruthenium deposited on an alumina support material thatcomprises macropores of greater than 50 nm in diameter.

It has also recently been discovered that materials consisting of Rusupported on a silica (SiO₂) support with “remnant structure” producedby deposition of an organic ruthenium compound on a silica support toform an organic ruthenium complex on or in the support, followed bydecomposition of the complex, have much higher activities andstabilities in the phthalate hydrogenation than reported Ru/Al₂O₃catalysts. WO 2004/046076, WO 2004/045767 and WO 2004/046078(ExxonMobil) disclose catalysts of Ru on silica supports prepared withthe remnant structures. US 2012/0296111 (BASF) discloses an eggshellcatalyst for hydrogenating carbocyclic aromatic compounds, such asphthalates, comprising a noble metal, such as ruthenium, deposited on asilica support material in which at least 90% of the pores present havea pore diameter of 6 to 12 nm. The catalysts may be prepared bydepositing ruthenium acetate on the silica support and then reducing.

Large pore extruded silica is a commercial catalyst support. US2010/0133148 (ExxonMobil) discloses a hydrodesulfurization catalystcomprising cobalt and molybdenum salts impregnated on large pore silicasupports. The catalyst is prepared by impregnating the silica supportwith a solution containing the metal ions, an organic additive, which isan alcohol or aminoalcohol, an organic acid and an inorganic acid. US2012/0184430 (Samsung) discloses the synthesis of a metal oxide supportmaterial, such as mesoporous silica, that has surface hydroxyl groups,including hydroxyl groups within its pores, and the preparation of acarbon dioxide reforming catalyst comprising a metal deposited onto thatsupport material. However, the use of large pore silica as an effectivesupport for ruthenium in a phthalate hydrogenation catalyst has notpreviously been achieved.

It has also been found that large pore silica support can facilitate themass transfer of large molecules of phthalate during catalyticreactions, which can be beneficial to the catalyst activity forphthalate hydrogenation to cyclohexanoates. However, in order to havelarge pores and high crush strength, the silica support is steam-treatedat high temperature. During the high temperature steam-treatments,improved extrudate crush strength and large porosity are accompanied bydecreases in hydroxyl group concentration and surface area of thesteamed silica support. As a consequence, known strong and large poresilica supports usually have low surface areas and low concentration ofhydroxyl groups due to high temperature steaming. Si—OH hydroxyl groupsare required for complexion to noble metals, such as ruthenium.Therefore, commercially available large pore silica are not particularlysuitable for use as ruthenium supports for phthalate hydrogenationcatalysts.

There remains a need for metal oxide-supported noble metal catalystswhich are highly active in phthalate hydrogenation. In particular, thereremains a need for a metal oxide support that can both facilitate themass transfer of large molecules of phthalate during catalytic reactionsand which has a high concentration of hydroxyl (Si—OH) groups forcomplexion to noble metals, such as ruthenium.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method for the synthesis ofa silica-supported noble metal catalyst, in particular asilica-supported ruthenium catalyst, in which a noble metal, preferablyruthenium, and optionally a chelating agent, is deposited onto a silicasupport that has been treated to add a fresh layer of silica onto thesurface of the silica support material. Advantageously, the treatment ofthe silica support increases the concentration of hydroxyl (Si—OH)groups on the surface. In one embodiment, the invention provides amethod for the preparation of a silica-supported noble metal (e.g.,ruthenium) hydrogenation catalyst comprising the steps of: (a)contacting a silica support with a silylating agent to coat at least apart of the silica support to produce a coated silica support; (b)calcining the coated silica support obtained in step (a) to produce atreated silica support; and (c) depositing a noble metal (e.g.,ruthenium) on the treated silica support obtained in step (b), such asby contacting the treated silica support obtained in step (b) with asolution comprising said noble metal (e.g., ruthenium) and an optionalchelating agent, for instance triethanolamine (TEA), to produce a noblemetal-containing silica support. The noble metal-containing silicasupport obtained in step (c) may be used as such as hydrogenationcatalyst or it may be subjected to further processing steps before beingused as a catalyst. The silica support used in step (a) is preferably alarge pore silica support, for example, produced by steam-treating. Thesilica may, for example, have a median pore size of at least 10 nm,especially at least 20 nm. Additionally or alternatively, the silicasupport may have a high crush strength, for example, a crush strength ofat least 800 g/mm, in particular at least 1000 g/mm. The method mayfurther comprise the step of steam-treating a silica to produce thesilica support used in step (a). The silylating agent is preferably apolysiloxane. In a preferred embodiment, the coated silica support ofstep (a) comprises at least a partial coating of a silylating agent on alarge pore silica support. The method of the present inventionoptionally further comprises drying the coated silica support preparedin step (a), prior to calcining in step (b). The method of the firstaspect of the invention optionally further comprises the step of dryingand/or (d) calcining the noble metal-containing silica support obtainedin step (c). The method optionally further comprises the step (e) ofactivating the catalyst for instance by contacting the noblemetal-containing silica support obtained in step (c) or (d) withhydrogen gas to form an activated catalyst.

In a second aspect, the invention provides a silica-supported noblemetal catalyst comprising a noble metal, preferably ruthenium, dispersedon a large pore silica support coated with a fresh silica layer. Inparticular, the invention provides a silica-supported noble metalhydrogenation catalyst comprising a noble metal, preferably ruthenium,dispersed on a silica support, wherein the median pore size of thecatalyst is at least about 10 nm, especially at least 20 nm.Advantageously, the catalyst of the second aspect of the presentinvention has a hydrogen to noble metal chemisorption ratio of at leastabout 0.50, especially at least 0.60. Advantageously, the catalyst ofthe second aspect of the invention has a crush strength of at least 800g/mm, in particular at least 1000 g/mm. The silica-supported noblemetal, preferably ruthenium, catalyst of the second aspect of theinvention may, for example, be prepared by the method of the firstaspect of the invention. The hydrogenation catalysts of the inventionare suitable for the catalysis of hydrogenation processes, for example,processes in which unsaturated hydrocarbons, such as aromatic compounds,are hydrogenated using hydrogen gas, especially for use in phthalatehydrogenation processes.

In a third aspect, the invention provides a method of hydrogenatingphthalates comprising the step of contacting a phthalate with a catalystof the second aspect of the invention or a catalyst obtainable orobtained by the method of the first aspect of the invention, forexample, in the presence of hydrogen gas.

In a fourth aspect, the invention provides a method of increasing theconcentration of hydroxyl (Si—OH) groups on the surface of a silicacatalyst support material, for example, a large pore silica support,such as a silica support having a median pore size of at least 10 nm,especially at least 20 nm, comprising the step of treating the silicasupport with a silylating agent. For example, the invention provides amethod of increasing, for example, repopulating, the hydroxyl groupconcentration of a silica support following steam treatment, the methodcomprising the step of treating the silica support by contacting with asilylating agent and then calcining.

In a fifth aspect, the invention provides a silica support having amedian pore size of at least 10 nm, especially at least 15 nm, and ahydroxyl group concentration sufficient to provide a catalyst havinghydrogen to noble metal chemisorption ratio of at least 0.5, especiallyat least 0.6, following deposition of the noble metal on the catalystsurface. Advantageously, the large pore silica support of the fifthaspect of the invention or prepared by the fourth aspect of theinvention has a crush strength of at least 800 g/mm, for example, atleast 1000 g/mm. The silica support of the fifth aspect of the inventionmay, for example, be prepared by increasing the hydroxyl (Si—OH) groupconcentration of a large pore silica support, such as a commerciallyavailable large pore silica support, or a silica support which has beensteam-treated, in accordance with the method of the fourth aspect of theinvention.

It has been found that treating silica supports with a silylating agentto form a silica coating or silica layer at the surface of the silicasupport improves the dispersion of noble metals, for instance ruthenium,onto the silica support. Without wishing to be bound by any theory, itis believed that treating a silica support that has been modified byhigh temperature steaming with a silylating agent, repopulates thehydroxyl groups on silica surface increasing the concentration ofhydroxyl groups for noble metal anchoring and restores the surface areaswhich were lost during the high temperature steaming. It has also beenfound that following coating of the silica supports with fresh layers ofactive silica, the properties of high crush strength and large porosityof a steam-treated silica support are preserved. Hydrogen chemisorptionexperiments have demonstrated that noble metal dispersion on a largepore silica support suitable for phthalate hydrogenation is greatlyimproved with treated silica supports of the invention. To formsilica-supported noble metal hydrogenation catalysts of the invention,the noble metal is preferably dispersed on a treated silica support witha chelation aid. Suitable chelation aids include amino alcohols, such astriethanolamine (TEA). For instance, TEA and Ru ions form complexes ofRu-TEA, which are anchored to the silica surface via the interactionswith hydroxyl groups of a silica support. The hydroxyl groups of thesilica support are the anchoring points for noble metal dispersion.

DETAILED DESCRIPTION OF THE INVENTION

The noble metal present in the catalyst of the present invention isselected from the group consisting of ruthenium, rhodium, palladium,platinum, and mixtures thereof, preferably ruthenium, most preferablyruthenium as the sole active metal.

The silica support used in step (a) typically has the property of highcrush strength as well as large pore sizes. Such silica support may beproduced by high temperature steaming. Silica catalyst supports havingthose properties are commercially available. The silica support used inthe present invention typically has a median pore size of at least about10 nm, for example, at least about 15 nm, especially at least about 20nm, such as at least about 25 nm. The silica support used in the presentinvention preferably has a median pore size of no more than about 300nm, for example, no more than about 200 nm, especially no more thanabout 150 nm. For example, the silica support may have a median poresize of from about 10 to about 100 nm, such as from about 15 nm to about80 nm. The median pore size may be determined by mercury porosimetry,for example, according to ASTM D4284-12. The pores may be approximatelyspherical or an irregular shape. The pore size is the largest dimensionof the pore, which is also known in the art as to as the “pore diameter”or “pore axis”. Typically the silica support has a crush strength of atleast 800 g/mm, for example, at least 1000 g/mm, preferably at least1200 g/mm. Crush strength is measured using the standard test method forsingle pellet crush strength of formed catalyst shapes set out in ASTMD4179-01. Suitable silica supports having the properties described aboveare described in U.S. Pat. No. 8,216,958 (ExxonMobil), the disclosure ofwhich is incorporated herein by reference.

The silica support used in the method of the invention can have anysuitable shape or form. Preferably, the silica support is in the form oftablets, pellets, extrudates, spheres, and the like and combinationsthereof. The extrudates may be of any cross section, for example,circular to form cylinders or tubes as well as trilobe or quadrulobe toform prisms. The silica support is typically a silica extrudate or asilica bead, preferably a silica bead.

If the silica support particles used in the method of the first aspectof the present invention are in the form of silica beads, spheres,tablets or pellets, the particle size distribution of said silicasupport may be determined by dry sieve analysis according to ASTMC136-96a. Said particle size distribution may be characterized by itsD10, D50 and D90 values where D50 corresponds to the size at which 50 wt% of the sample is smaller and 50 wt % of the sample is larger. In thepresent invention, D50 is used to characterize the silica supportaverage particle size or average diameter. The width or span of theparticle size distribution is calculated as (D90−D10)/D50. The particlesize distribution of a population of particles used in the presentinvention is typically relatively narrow, for instance with a span equalto or lower than 2, preferably equal to or lower than 1.5, morepreferably equal to or lower than 1, in particular equal to or lowerthan 0.5 such as about 0.2.

If the silica support particles used in the method of the first aspectof the present invention are the form of extrudates, i.e., in the formof elongated shapes having a substantially constant cross section whichcorresponds to the hole of the extrusion die, the silica supportparticles may be characterized by an average length, an average diameterand an average aspect ratio. According to the present invention, thelength of an extrudate corresponds to the extruded length of saidextrudates, the diameter of an extrudate corresponds to the outsidediameter of said extrudate cross section, i.e., the diameter of thesmallest circle circumscribing the cross section, and the aspect ratioof an extrudate corresponds to the ratio of its length on its diameter.Thus, for example, for a cylindrical extrudate, the diameter of theparticle corresponds to the diameter of the disc cross section. For anextrudate having an elliptic cross section, the diameter of the particleis the major axis of the ellipse, i.e., the line segment that runsthrough the center and both foci, with ends at the widest points of theextruded elliptical cross section. For a symmetric quadrulobe extrudate,the diameter is the highest dimension of the quadrulobe section, i.e.,the longest distance, in a straight line between two points on thequadrulobe cross section and its center. The diameter of an extrudate issubstantially constant, as the cross section of the extrudate isdictated by the size of the hole in the extrusion die. The averagelength, average diameter, and average aspect ratio of the extrudatesilica support particles of the present invention may be determined byoptical scanner imaging using ALIAS Image Analysis System (Cascade DataSystem). The sample size is typically of 150 to 250 particles, withoutsample preparation per se. The average length and average diameter arethe numerical averages (arithmetic means) of the measured individuallengths and diameters while the aspect ratio is the fraction of saidaverage length on said average diameter. The average length of theextrudate silica support particles used in the method of the firstaspect of the invention can vary widely and is not critical. In thepresent invention, the average length to diameter aspect ratio of saidextrudate silica support particles is usually at least 1, most oftenhigher than 1, typically at least about 2, in particular at least about2.5, for example, at least about 3. Said average aspect ratio is usuallyat most about 10, typically at most about 8, for instance at most about5.

The average diameter of the silica support particles used in the methodof the first aspect of the invention, whether beads, spheres, tablets orpellets, extrudates or other forms, is generally in the range of fromabout 0.8 mm to about 10 millimeters (mm), preferably in the range offrom about 1.0 mm to about 5 mm, and more preferably in the range offrom about 1.2 mm to about 3 mm, such as from about 1.3 mm to about 2mm. Preferably, the average diameter of the particles is no more thanabout 2.4 mm, for example no more than about 2.2 mm, especially no morethan about 2.0 mm. In some embodiments, the silica support consists ofparticles having an average diameter of less than about 2.0 mm, forexample, no more than about 1.8 mm, especially no more than about 1.7mm. Typically, the particles have an average diameter of at least 0.7mm. Preferably, the silica support consists of particles having anaverage diameter of from about 0.8 mm to about 2.2 mm, especially fromabout 1.0 mm to about 2.0 mm, for example, from about 1.2 mm to about1.8 mm. The catalyst of the second aspect of the invention typicallyconsists of particles of substantially the same size as the silicasupport listed above. For example, a catalyst of the second aspect ofthe invention based on silica support particles in the form of beads,spheres, tablets, pellets or extrudates, preferably consists ofparticles having an average diameter of from about 0.7 mm to about 2.4mm, especially from about 0.8 mm to about 2.2 mm, for example, fromabout 1.0 mm to about 2.0 mm. The average diameter of the particles ofsupport or catalyst may, for example, be measured by dry sieve analysisand/or optical scanner imaging as appropriate.

The silica support used in the method of the invention hasadvantageously been steam treated. The method of the first or thirdaspects of the invention optionally comprises the additional step ofheating a silica, for example, a silica extrudate, in the presence ofsteam prior to step (a). The silica material is optionally heated to atemperature of at least 400° C., such as at least about 450° C., forexample, a temperature in the range of from about 500° C. to about 800°C. in the presence of steam, for example, in an atmosphere comprising atleast 5 wt % steam, especially at least 10 wt % steam. The step of steamtreating a silica material advantageously increases the crush strengthand/or the pore size of the silica and can therefore be used to preparea silica support having a large pore size, e.g., a pore size of 10 nm orgreater, especially 15 nm or greater, and a high crush strength, e.g., acrush strength of 800 g/mm or greater, especially 1000 g/mm or greater.

The silica support preferably has a silica content of at least 60 wt %,for example, at least 80 wt %. In addition to silica, the silica supportmay, for example, also comprise alumina however alumina is preferably aminor component. Accordingly, the silica support preferably comprises nomore than 40 wt % alumina, for example, no more than 20 wt % aluminaespecially, no more than 10 wt % alumina.

The silica support used in the methods of the invention typically has apore volume of at least about 0.2 ml/g, for example, at least about 0.5ml/g, especially at least about 0.6 ml/g. The silica support typicallyhas a pore volume of no more than about 3.0 ml/g, for example, no morethan about 2.0 ml/g, especially no more than about 1.5 ml/g. Forexample, the silica support typically has a pore volume in the range offrom about 0.2 ml/g to about 1.2 ml/g, such as from about 0.3 to about1.0 ml/g or to about 0.8 ml/g. The pore volume may be determined bymercury porosimetry, for example, according to ASTM D4284-12. A silicasupport for use in preparing the treated silica support used in thepresent invention generally has a surface area, measured by theBrunauer, Emmett, Teller (BET) method, ASTM D1993, in the range of fromabout 20 m²/g to about 400 m²/g, preferably in the range of from about40 m²/g to about 300 m²/g, and more preferably in the range of fromabout 50 m²/g to about 200 m²/g.

The silylating agent used in step (a) may be any suitablesilicon-containing compound that effectively treats a silica support soas to repopulate the hydroxyl (Si—OH) groups on the surface of thesilica support. Preferably, the silylating agent at least partiallycoats the silica support with silica, typically after calcination.Suitable silylating agents for use in treating the silica supportaccording to the present invention include monomeric or oligomericcompounds having a plurality of siloxane groups attached to an organiccore, in particular polysiloxanes and organosilicon compounds comprisingmultiple siloxane groups, such as polyalkyl siloxanes andpoly(alkylaryl) siloxanes, most preferably poly(alkylaryl) siloxanes.The term “polysiloxane” as used herein refers to compounds havingmultiple siloxane (O—Si—O) functionality. Suitable polysiloxanes includepolymerised siloxanes having an inorganic silicon-oxygen backbone(⋅⋅⋅—Si—O—Si—O—Si—O-⋅⋅⋅) with organic side groups attached to thesilicon atoms, i.e., polymers with the chemical formula [R₂SiO]_(n),where R is an organic group such as alkyl, in particular C₁₋₆ alkyl,especially C₁₋₄ alkyl, such as methyl or ethyl, and/or aryl, especiallyphenyl. Suitable examples of polysiloxanes are poly(C₁₋₄ alkyl)siloxanes such as polydimethylsiloxane (PDMS); poly(C₁₋₆ alkylphenyl)siloxanes, such as phenyl methyl polysiloxane (PPMS), full IUPAC name1,1,5,5,5-hexamethyl-3-phenyl-3-((trimethylsilyl)oxy)trisiloxane; andsilicone resins that comprise crosslinked matrices of branched andcage-like oligosiloxanes, for example, of the formula R_(n)SiX_(m)O_(y),where R is a non-reactive substituent, usually alkyl or aryl, and X is afunctional groups such as hydroxy. The treating agent may, for example,be an organosilicon compound selected from compounds having thefollowing formulae: SiR_(y)X_(4-y), (R_(w)X_(3-w)Si)₂.Z,[SiR_(m)OX_(2-m)]_(n), [SiR_(m)X_(2-m)]_(n), and combinations of any twoor more thereof, wherein y=1 to 4; w=1 to 3; m=1 to 2; n>2,preferably >5, and more preferably in the range of from 10 to 5,000,000;R=alkyl, aryl, H, alkoxy, aryloxy, arylalkyl, alkylaryl; when y>=2 orw>=2 or m=2, R can be the same or different and is independentlyselected from the groups listed; X=halide; and Z=oxygen or imino oralkylimino or alkanoylimino. Suitable organosilicon compounds includethose described in U.S. Pat. No. 7,030,053, the disclosure of which isincorporated herein by reference (see column 4, lines 15 to 44), forexample, tetraethoxysilane.

Contacting step (a), wherein the silica support is contacted with thesilylating agent, can be conducted by any manner or method that providesfor an at least partially coated silica support that can be utilized inpreparing a catalyst composition of the present invention. Thecontacting may, for example, comprise the step of impregnating and/ormixing the silylating agent, typically in solution, with the silicasupport. The solution may be an aqueous solution, an alcohol-containingsolution, or a hydrocarbon solution of the treating agent. The treatmentmay, for example, involve contacting the silica support with a solutionof the silylating agent in an organic solvent. The organic solvent maybe an alkane solvent, for example, a C₃ to C₁₂ alkane or mixture of C₃to C₁₂ alkanes, such as hexane, heptane, octane, nonane, decane,undecane, dodecane and mixtures thereof. A preferred impregnationtechnique is “incipient wetness impregnation” that includes essentiallycompletely filling of the pores of the silica support with a solution ofthe silylating agent. The concentration of the silylating agent in thesolution can range upwardly to the solubility limit of the silylatingagent in the solvent. Generally, the concentration of the silylatingagent in the solution can be in the range of from about 1 wt % to about50 wt %, preferably in the range of from about 2 wt % to about 30 wt %,and more preferably in the range of from about 4 wt % to about 20 wt %.Said contacting step may be made at any suitable temperature andpressure, for instance at room temperature and atmospheric pressure.

Steps (a) and (b) result in an at least partially coated silica support,typically with one or more fresh silica layers, by the deposition oflayers of polysiloxane compounds followed by a calcining step. Saidtreated silica support includes fresh silica on at least part of thesurface of the silica support. Generally, a weight ratio of fresh silicacoating to underlying silica support is in the range of from about0.01:1 to about 0.30:1, preferably in the range of from about 0.03:1 toabout 0.25:1, and more preferably in the range of from about 0.05:1 toabout 0.20:1. Typically the additional silica added via the treatmentsteps (a) and (b) constitutes from about 8% to about 12% of the totalweight of the treated silica support.

Generally, the amount of silylating agent deposited on the silicasupport in the methods of the present invention is in the range of fromabout 5 wt % to about 50 wt % based on the total weight of the supportfollowing contact with the silylating agent, preferably in the range offrom about 10 wt % to about 40 wt %, and more preferably in the range offrom about 12 wt % to about 35 wt %.

After contacting the silica support with a silylating agent in step (a)and before calcining step (b), the resulting coated silica support(containing a silylating agent) is optionally subjected to a dryingstep. The drying step may be carried out at a temperature in the rangeof from about 40° C. to about 180° C., preferably in the range of fromabout 5° C. to about 150° C., and more preferably in the range of fromabout 50° C. to about 130° C. The drying step may be performed underreduced pressure or under atmospheric pressure, in an inert atmosphereor in air, preferably in an inert atmosphere such as under nitrogen andunder atmospheric pressure. The drying can also be promoted by passing agas stream over or through the material to be dried, for example, air ornitrogen, preferably nitrogen. The drying time depends upon the desireddegree of drying and the drying conditions and is preferably in therange of from 1 hour to 30 hours, preferably from 2 hours to 10 hours.

In addition to the optional drying step, the preparation of a treatedsilica support comprises a calcining step (b), conducted under calciningconditions, such as exposure to a high temperature, for example, in therange of from about 250° C. to about 1000° C., preferably in the rangeof from about 300° C. to about 900° C., and more preferably in the rangeof from about 400° C. to about 700° C. The calcining step is preferablyconducted in the presence of oxygen, for example, in air or in an oxygenenriched environment comprising at least 30% by volume oxygen. Thecalcining step may also include heating in an inert environment, forexample, under nitrogen, followed by calcination under a gas mixturecomprising an inert gas and oxygen or air, such as a mixture of nitrogenand oxygen. During calcining, substantially all volatile matter (e.g.,water and carbonaceous materials) is removed. The coated silica supportis subjected to calcination to form a treated silica support prior tocontacting with the noble metal in step (c). The step (a) of contactinga silica support with a silylating agent together with the calcinationstep (b) and optional intermediate drying step, are collectivelyreferred to as a “treatment step” that produces a treated silicasupport.

Advantageously, the treatment of the silica support in steps (a) and (b)increases the concentration of hydroxyl groups on the silica support byat least 1 Si—OH group by per nm², for example, by at least 1.5 Si—OHgroup per nm². Silica Si—OH concentrations can, for example, be measuredby reacting the active hydrogen of the hydroxyl groups of a knownquantity of silica with a C₂H₅MgBr ethyl magnesium bromide Grignardreagent to produce ethane C₂H₆. The volume of ethane evolved can be usedto calculate active hydrogen of OH groups of the silica support.Alternatively, a calibration curve of standard silica materials withknown OH concentrations can be made using Fourier Transform InfraredSpectroscopy (FTIR) and then the FTIR of a silica with an unknown OHconcentration can be compared against the calibration curve.Advantageously, the treatment of the silica support increases theconcentration of hydroxyl groups on the silica support such that themaximum hydrogen to noble metal chemisorption ratio (hereinafter alsoreferred to as H/noble metal chemisorption ratio) that can be achievedfollowing noble metal deposition is increased by at least 0.1 comparedto the untreated silica support. As discussed in more detail below, thehydrogen to noble metal chemisorption ratio is an indication of thelevel of dispersion of the metal on the support and an indication of theavailability of the metal atoms as catalytic sites. High hydrogen tonoble metal chemisorption ratios are thus indicative of higher catalyticactivity. Advantageously, the treatment of the silica support in steps(a) and (b) increases the concentration of hydroxyl groups on the silicasupport such that a hydrogen to noble metal chemisorption ratio inexcess of 0.5 can be achieved after deposition of noble metal,preferably ruthenium, onto the silica support. Advantageously, thetreatment step increases the surface area of the support as measured bythe Brunauer, Emmett, Teller (BET) method, ASTM D1993. For example, thetreated silica support produced in step (b) may have a BET surface areaof at least about 10 m²/g, preferably at least about 20 m²/g, especiallyat least about 25 m²/g greater than the untreated silica support used instep (a). In some embodiments, the BET surface area is increased by atleast about 30 m²/g. Advantageously, the treated silica support has asurface area, measured by the BET method, of at least about 30 m²/g,preferably at least about 40 m²/g, and more preferably at least about 45m²/g. In some embodiments the treated silica support has a surface area,measured by BET method of at least about 50 m²/g. Typically, the surfacearea as measured by the BET method is 300 m²/g or less, for example, 200m²/g or less, such as 150 m²/g or less.

The step (c) of depositing a noble metal on the treated silica supportto form a noble metal-containing silica support comprises contacting thetreated silica support obtained in step (b) in any contacting mannerwith a noble metal, typically in the form of a precursor compound ofsaid noble metal. Suitable precursor compounds are noble metal compoundswhich can be converted into metallic compounds. Examples of suitablecontacting methods include, but are not limited to, impregnation,mixing, immersion, and the like. Generally, depositing a noble metal ona treated silica support according to a process of the present inventioncomprises an impregnation technique. Generally, the treated silicasupport is impregnated with a noble metal precursor dissolved in anaqueous solution such as deionized water, by immersing the treatedsilica support in the solution of the noble metal precursor, forexample, by incipient wetness impregnation in which the pores of thetreated silica support are filled with the solution. The treated silicasupport can also be sprayed with an impregnating solution containing adissolved noble metal precursor component. The amount of noble metalprecursor utilized in the method of the first aspect of the presentinvention is such as to provide a concentration of said noble metal onthe treated silica support that is suitable to catalyze hydrogenationreactions, for example, the hydrogenation of phthalates intocyclohexanoates. Typically, the concentration of noble metal in acatalyst of the second aspect of the present invention is in the rangeof from about 0.1 wt % to about 5 wt % based on the total weight of thecatalyst composition, preferably in the range of from about 0.1 wt % toabout 2 wt %, and more preferably in the range of from about 0.2 wt % toabout 1 wt %, especially from about 0.5 wt % to about 0.8 wt %, based onthe total weight of the catalyst composition. Generally, theconcentration of the noble metal precursor in the impregnating solutionis in the range of from about 0.01 Molar (M) to about 1.0 M, preferablyin the range of from about 0.01 M to about 0.20 M, and more preferablyin the range of from about 0.02 M to about 0.10 M, especially from about0.03 M to about 0.08 M. Examples of a suitable solvent of theimpregnating solution include, but are not limited to, deionized water,an alcohol and combinations thereof.

The noble metal may be deposited on the surface of the treated silicasupport in any form, including salt forms, organo-metal compounds, metaloxides or complexes comprising noble metal atoms or ions. The noblemetal is typically deposited onto the treated silica support as a salt,for example, in a suitable solvent, such as water or another polarprotic solvent, such as C₁-C₄ alkanols, for instance methanol, ethanol,n-propanol or isopropanol. Suitable noble metal salts include nitrate,nitrosyl nitrate, halide (typically bromide, chloride or iodide) andacetate salts, in particular nitrosyl nitrate. Ruthenium nitrosylnitrate salts are especially preferred. Alternatively, the noble metalmay be deposited onto the treated silica catalyst support by contactingthe treated silica support with noble metal oxide, for instanceruthenium oxide.

Advantageously, the noble metal is deposited on the silica support inthe form of to a salt and in the presence of a chelating agent, forexample, as a solution of a noble metal salt and a chelating agent, morepreferably as a noble metal-chelating agent complex, for example, as aruthenium-chelating agent complex. The formation of a noblemetal-chelating complex typically inhibits undesired interactions amongnoble metal atoms, thus preventing noble metal particle agglomerations.The chelating agent advantageously acts as a dispersion aid.

The chelating agents for use in the methods of the invention include atleast one and in particular from 1 to 6 nitrogen-containing functionalgroups selected from amine and imine functional groups (i.e., aminoand/or imino groups), such as from 1 to 6 secondary or tertiary aminefunctional groups. Preferably the chelating agent also includes at leastone carboxylic acid and/or hydroxyl functional group, preferably from 1to 6 carboxylic acid and/or hydroxyl functional groups, more preferablyfrom 2 to 6 carboxylic acid and/or hydroxyl functional groups. In aparticular embodiment, the chelating agent has from 2 to 20 carbonatoms, for example, from 4 to 15 carbon atoms. Advantageously, thechelating agent comprises at least one carboxylic acid and/or hydroxylfunctional group as well as at least one nitrogen-containing functionalgroup selected from amine and imine functional groups (preferably aminefunctional group), and has from 2 to 20 carbon atoms. Especiallysuitable chelating agents are amino alcohols and/or amino carboxylicacids comprising 1 to 6 carboxylic acid and/or hydroxyl functionalgroups, preferably at least 2 carboxylic acid and/or hydroxyl functionalgroups, more preferably 2 to 6 carboxylic acid and/or hydroxylfunctional groups and 1 to 6 nitrogen-containing functional groupsselected from amine and imine groups, especially 1 to 6 amine groups,more particularly 1 to 6 secondary or tertiary amine groups, and 2 to 20carbon atoms, preferably from 2 to 15 carbon atoms, for example, from 2to 10 carbon atoms. Advantageously, the chelating agent comprises 1 to 6hydroxyl functional groups, preferably 2 to 6 hydroxyl functionalgroups, and 1 to 6 amine or imine functional groups, especially 1 to 6amine functional groups, preferably 1 to 6 secondary or tertiary aminegroups, and 2 to 20 carbon atoms, in particular from 2 to 15 carbonatoms, especially 2 to 10 carbon atoms. Suitable chelating agent includethose described in U.S. Pat. No. 3,761,428 (Institute Francais duPetrole) (see col. 1, lines 51 to 64) and those described in US2010/0133148 (ExxonMobil) (see paragraphs [0038] to [0042]), thedisclosure of both of which is incorporated herein by reference.Preferred chelating agents for use in the methods of the inventioninclude C₂ to C₂₀ amino alcohols, including dialkanolamines, such asdiethanolamine and dialkanoldiamines, and trialkanolamines, for instancetriethanolamine (TEA). Other suitable chelating agents are aminocarboxylic acids, including polyamino carboxylic acids, aminopolycarboxylic acids, such as nitrilotriacetic acid (NTA), and polyaminopolycarboxylic acids, such as ethylenediaminetetraacetic acid (EDTA), aswell as polyamines, such as guanidine. Preferred chelating agents areTEA and EDTA, with TEA being especially preferred. Chelating agentscomprising amine or imine functional groups have been found to formcomplexes with noble metal ions, such as Ru-TEA. Those complexes areadvantageously anchored to the silica surface via the interactions withthe hydroxyl groups (Si—OH) of the silica support. It has also beenfound that chelating agents comprising carboxylic acid or hydroxylfunctional groups as well as at least one nitrogen-containing functionalgroup selected from amine and imine groups form particularly stronginteractions with the hydroxyl groups (Si—OH) of the silica support.Thus, chelating agents comprising amine and/or imine functional groupsas well as carboxylic acid and/or hydroxyl functional groups have beenfound to be the most effective dispersion aids for noble metals.Typically, the noble metal is deposited on the silica support in thepresence of an excess of chelating agent, for example, at least 5 molarequivalents of chelating agent, especially at least 10 molar equivalentsof chelating agent, such as at least 15 molar equivalents of chelatingagent.

After depositing the noble metal on the treated silica support, theresulting noble metal-containing silica support is optionally subjectedto a washing and/or drying step. This washing step typically uses water.This drying step typically includes a temperature generally in the rangeof from about 20° C. to about 200° C., preferably in the range of fromabout 50° C. to about 175° C., and more preferably in the range of fromabout 75° C. to about 150° C. The drying step may be performed underreduced pressure or under atmospheric pressure, in an inert atmosphereor in air, most often in air and under atmospheric pressure. The dryingcan also be promoted by passing a gas stream over or through thematerial to be dried, for example, air or nitrogen. The drying timedepends upon the desired degree of drying and the drying conditions andis preferably in the range of from 1 hour to 30 hours, preferably from 2hours to 10 hours.

Further optionally, and alternatively or additionally to the dryingstep, the preparation of the silica-supported noble metal catalyst maycomprise a calcination step (d) of the noble metal-containing silicasupport under a calcining condition, such as exposure to a hightemperature, for example, in excess of about 200° C., preferably inexcess of about 240° C., and more preferably in excess of about 260° C.,for example, from about 200° C. to about 600° C., such as from about240° C. to about 400° C. During calcining, substantially all volatilematter (e.g., water and carbonaceous materials) is removed. The optionalcalcination step (d) performed after contacting of the treated silicasupport with the noble metal is typically carried out at a lowertemperature than the calcination step (b) performed after contacting thesilylating agent and the silica support in step (a). For example, theoptional calcination step (d), performed after deposition of the noblemetal on the coated silica support, may be performed at a temperature ofat least about 100° C., for example, at least about 200° C. less thanthe temperature of the calcination step (b) performed prior to thedeposition of the noble metal on the silica support. The calcinationstep (d) is usually conducted in air.

Advantageously, the silica-supported noble metal catalyst produced bythe process of the present invention is subjected to an optionalactivation step (e), in which the noble metal-containing silica supportobtained in step (c) or (d) is contacted with hydrogen gas. Typicallythe activation step (e) takes place in an atmosphere comprising at least60% by volume hydrogen, for example, at least 80% by volume hydrogen,especially at least 95% by volume hydrogen, for example, an atmosphereof essentially 100% hydrogen. Any gas present in addition to hydrogen ispreferably an insert gas such as nitrogen. Typically the contacting withhydrogen gas takes place at an elevated temperature such as atemperature of at least about 200° C., for example, a temperature of atleast about 300° C., especially a temperature of at least about 400° C.For example, the contacting with hydrogen gas takes place at atemperature of from about 300° C. to about 650° C., such as from about400° C. to about 550° C. Typically the hydrogen pressure is slightlyabove ambient pressure, such as a pressure of from about 10 kPa gauge toabout 100 kPa gauge, such as about 34 kPa gauge (5 psig), i.e., around136 kPa absolute pressure. Typically, the silica-supported noble metalcatalyst may be contacted with hydrogen gas for at least about 1 hour,such as for at least about 2 hours. Preferably, the silica-supportednoble metal catalyst is contacted with hydrogen gas for no more thanabout 5 hours. Contacting of the silica-supported noble metal catalystwith hydrogen gas for about 2.5 hours has been found to be sufficient tofully activate the catalyst.

The activation step (e) may optionally be followed by a passivation step(f). Such a passivation step (f) can for instance be conducted bytreating the catalyst briefly in an oxygen-containing gas, for example,air, but preferably with an inert gas mixture comprising from 1 to 10volume percent of oxygen. It is also possible to use CO₂ or CO₂/O₂mixtures. The passivation step may for instance be conducted at roomtemperature under atmospheric pressure for a few hours.

Advantageously, the catalyst of the second aspect of the inventionand/or the catalyst produced by the method of the first aspect of theinvention, has a hydrogen to noble metal chemisorption ratio, H/noblemetal chemisorption ratio, preferably H/Ru chemisorption ratio, of atleast about 0.50, especially at least about 0.60, preferably at leastabout 0.65. The H/noble metal chemisorption ratio is the molar ratio ofhydrogen atoms absorbed on the catalyst for each noble metal atom andthus is a measure of the dispersion of the ruthenium on the catalyst. AH/noble metal chemisorption ratio of 1 would indicate that 100% of noblemetal atoms are bound to a hydrogen atom after chemisorption of hydrogenand are thus fully dispersed, such that each noble metal atom isaccessible for hydrogen binding. A H/noble metal chemisorption ratio of0.5 indicates that only 50% of the noble metal atoms are able to bind tohydrogen, the remainder being inaccessible. Suitable conventionalvolumetric chemisorption techniques which can be employed to measurehydrogen chemisorption of the catalysts of the invention are discussedin Structure of Metallic Catalysts, J. R. Anderson, Academic Press,1975, chapter 6. The hydrogen to noble metal chemisorption ratio can,for example, be calculated by reduction of a sample of silica-supportednoble metal catalyst that contains a known quantity of noble metal withhydrogen and determining the quantity of hydrogen absorbed onto thecatalyst, for example, by extrapolation of the isothermal profile tozero hydrogen pressure, after reduction of the sample at 200° C. inhydrogen for 30 minutes.

Advantageously, the catalyst produced in the method of the inventionsubstantially retains the pore size of the silica support used in itspreparation. Preferably, the catalyst of the second aspect of theinvention and/or the catalyst produced in the method of the first aspectof the invention has a median pore size of at least about 10 nm, forexample, at least about 15 nm, especially at least about 20 nm, such asat least about 25 nm. Advantageously, the catalyst produced in themethod of the first aspect of the invention has a median pore size atleast about 75%, for example, at least about 80%, especially at leastabout 85%, such as at least about 90% of that of the large pore silicasupport used in step (a).

The catalyst of the second aspect of the invention or the catalystproduced by the method of the first aspect of the invention isespecially suitable as a hydrogenation catalyst, in particular for thehydrogenation of unsaturated hydrocarbons, especially phthalates, forinstance dimethyl phthalate, di-2-propylheptyl phthalate,di-2-ethyl-hexyl phthalate, dioctyl phthalate, or diisononylphthalate.

In one embodiment of the second aspect of the invention, there isprovided a silica-supported noble metal catalyst, preferably asilica-supported ruthenium catalyst, wherein the median pore size of thesilica support is at least 10 nm, especially at least 15 nm; thecatalyst has an H/Ru of at least 0.50, especially at least 0.60; andoptionally the catalyst has a crush strength of at least 800 g/mm, forexample, at least 1000 g/mm.

In one embodiment, the method of the first aspect of the invention is amethod of producing a hydrogenation catalyst which comprises the stepsof: providing a silica support having a median pore size of at least 10nm, especially at least 20 nm, for example, by steam-treating a silicaextrudate or other silica material; (a) contacting the silica supportwith a silylating agent to form a coated silica support; optionallydrying the coated silica support; (b) calcining the coated silicasupport to form a treated silica support; (c) depositing ruthenium onthe treated silica support of step (b) by contacting the treated silicasupport with a solution comprising ruthenium and a chelating agentwherein the chelating agent comprises at least one carboxylic acid orhydroxyl functional group as well as at least one nitrogen-containingfunctional group selected from amine and imine groups, to produce aruthenium-containing silica support; optionally drying theruthenium-containing silica support; optionally (d) calcining theruthenium-containing silica support to form a silica-supported rutheniumcatalyst; and optionally (e) activating the silica-supported rutheniumcatalyst by contacting the silica-supported ruthenium catalyst withhydrogen gas.

In a further embodiment, the method of the first aspect of the inventionis a method of producing a phthalate hydrogenation catalyst whichcomprises the steps of: providing a silica support having a median poresize of at least 10 nm, especially at least 20 nm, for example, bysteam-treating a silica extrudate or other silica material; (a)contacting the silica support with a polysiloxane silylating agent toform a coated silica support; drying the coated silica support of step(a); (b) calcining the dried coated silica support to form a treatedsilica support; (c) depositing ruthenium on the treated silica supportof step (b) by contacting the treated silica support with a solutioncomprising a ruthenium salt and a C₂₋₆ amino alcohol chelating agent toform a ruthenium-containing silica support; optionally drying theruthenium-containing silica support; (d) calcining theruthenium-containing silica support to form a silica-supported rutheniumcatalyst; and optionally (e) activating the silica-supported rutheniumcatalyst by contacting the silica-supported ruthenium catalyst withhydrogen gas. The catalyst may, for example, be made by impregnation ofan aqueous solution of a ruthenium salt, advantageously rutheniumnitrosyl nitrate, in the presence of TEA onto a silica-coated large poresilica support. In the catalysts prepared by the method of theinvention, the ruthenium may, for example, be dispersed in the form ofan aqueous solution of ruthenium-TEA complex on a DOW 550 silica-coatedlarge pore silica support.

EXAMPLES OF THE INVENTION

The following examples illustrate the present invention. Numerousmodifications and variations are possible and it is to be understoodthat within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described herein.

Commercially available, large pore, RT-235, silica support in the formof cyclindrical extrudates having an average diameter of about 1.4 mm (1/18 inch), manufactured by Albemarle, was coated with phenyl methylpolysiloxane (DOW 550). The coated silica support was dried and calcinedbefore its use as a treated silica support for the deposition ofruthenium by impregnation with a Ru-TEA solution. The RU-TEA impregnatedsilica samples were then dried and calcined in air. As a comparison,untreated RT-235 was also impregnated with a Ru-TEA solution, dried andcalcined under the same conditions. The hydrogen chemisorptions of bothresulting catalysts were compared.

Example 1—Preparation of Treated RT-235 Support

RT-235 silica extrudates were used as a starting material for thedeposition of a SiO₂ coating of DOW 550 phenyl methyl polysiloxanesilicone oil. In a fume hood, RT-235 silica extrudates were impregnatedwith a decane solution containing 7.8 wt % of DOW 550 silicone. Thesample was placed in a drying oven then purged with nitrogen for 1 hourto remove air before drying. The sample was dried at about 70° C. (160°F.) overnight in nitrogen environment. After drying, the sample wasplaced in a box furnace for calcination. The calcining furnace washeated in the presence of N₂ from room temperature to about 540° C.(1000° F.) at 2.8° C./min (5° F./min). The furnace was held at about540° C. (1000° F.) for 1 hour. The calcining atmosphere was thengradually switched from N₂ to a mixture gas containing 40% oxygen and60% nitrogen in a period of 2 hours. The final calcining treatment wascarried out in this 40% oxygen/60% nitrogen gas mixture at about 540° C.(1000° F.) for 6 hours. Typically, between about 8% and about 12% byweight of the treated silica support after air calcination was silicaderived from the DOW 550 silicone oil coating. The treated RT-235 silicasupport is abbreviated as “DOW-550 coated RT-235”.

Example 2—Characterization of Untreated and Treated Silica Supports

The untreated (RT-235) and treated (DOW-550 coated RT-235) silicasupports were characterized by their BET surface area (ASTM D1993),median pore size (mercury porosimetry according to ASTM D4284-12), andpore volume (mercury porosimetry according to ASTM D4284-12). SaidRT-235 and DOW 550 coated RT-235 silica supports were also compared to aconventional silica support sold by PQ Corporation, referred to as PQSiO₂. The results are summarized in Table 1 below.

TABLE 1 BET Pore Median pore surface area vol diameter Silica supports(m²/g) (ml/g) (nm) PQ SiO₂ 205 1.1 17.4 RT-235 SiO₂ 98 0.71 27.7 DOW 550coated RT-235 168 0.93 21.0

It can be seen from Table 1 that the treatment of RT-235 silica supportwith DOW 550 increased the BET surface area from 98 to 168 m²/g. The DOW550 silica coating also improved the pore volume of the RT-235 silicasupport from 0.71 ml/g to 0.93 ml/g.

Example 3—Ru/SiO₂ Catalyst Preparations by Ruthenium Impregnation andCalcination on Treated and Untreated RT-235 Supports

Silica-supported ruthenium catalysts were prepared by incipient wetnessimpregnation. Untreated (RT-235) and treated (DOW-550 coated RT-235)silica supports were used as catalyst supports. The ruthenium precursorcompound used in the catalyst preparation was ruthenium nitrosylnitrate. The chelation aid added in the impregnation solution wastriethanolamine (TEA). The mixture solution was prepared by addingappropriate amounts of TEA and ruthenium nitrosyl nitrate into distilledH₂O. The volume of the impregnation solution used was about 95% of thesolution absorption capacity of the silica support. For example, 8.37 gof ruthenium nitrosyl nitrate solution containing 1.5 wt % Ru was addedto 3.73 g of triethanolamine (TEA). 10 g of water was added to themixture of Ru-TEA. The solution was stirred until it was clear. Thetotal solution volume prepared was about 23.8 ml. The concentration ofRu in the solution was 0.05 M and TEA was 1.05 M. The molar ratio of TEAto Ru was 21. 25 g of silica supports was used in the catalystpreparation. After deposition of the ruthenium on the silica supports,the ruthenium-containing silica supports were dried in air at 100° C.for 12 hours and calcined in air at 275° C. for 1 hour with ramping rateof 5° C./min to produce a silica-supported ruthenium catalyst. The airflow rate inside the calciner was adjusted at 5 volume/volumecatalyst/minute. The silica-supported ruthenium catalysts contained 0.5%Ru, with respect to the total weight of catalyst.

Example 4—Activation of the Ru/SiO₂ Catalysts by Reduction andPassivation

The reduction reactor was ramped from room temperature to 425° C. at 5°C./min rate. The silica-supported ruthenium samples prepared accordingto Example 3 were reduced at 425° C. for 2.5 hours with 100% hydrogen.The hydrogen pressure was 34 kPa gauge (5 psig) adjusted by backpressureregulator plus atmospheric pressure. The reduced catalysts were allowedto cool down to room temperature in a H₂ flow. When the temperature ofthe reactor reached room temperature, the H₂ flow was replaced with amixture of 1% air balanced with N₂. The catalyst passivation was carriedout at room temperature for 2 hours. The gas flow of 1% air/N₂ then wasadjusted at 5 volume/volume catalyst/minute.

Example 5—Hydrogen Chemisorption and Elemental Analysis

A Micromeritics ASAP 2020 Chemi system was used to measure hydrogenchemisorption and calculate the Ru dispersion of the silica-supportedruthenium catalysts prepared according to Example 3. Thesilica-supported ruthenium hydrogenation catalyst samples were driedunder helium at 200° C. for 30 minutes to remove any moisture. Samplereduction was carried out at 200° C. in hydrogen for 30 minutes. Theramping rate was controlled at 5° C./min. After reduction, the samplechamber was evacuated at 200° C. for 1 hour, then the reactor was cooleddown to room temperature while the system was still under vacuum. Thehydrogen isothermal was measured at room temperature. The H/Ruchemisorption ratio was calculated by extrapolation of the isothermalprofile to zero hydrogen pressure.

The residual carbon and nitrogen contents of the silica-supportedruthenium catalysts of Example 3 were determined by chemiluminescence.The ruthenium and sodium contents of the catalysts were determined byX-ray fluorescence (XRF).

The results of the hydrogen chemisorption and elemental analysis aresummarized in Table 2 below.

TABLE 2 H/Ru Catalyst C and N Ru and Na chemisorption supports (%) (%)ratio RT-235 C: 2.8 Ru: 0.53 0.39 N: 1.0 Na: 0.19 DOW 550 C: 2.9 Ru:0.48 0.70 coated RT-235 N: 1.1 Na: 0.22

The results of Table 2 show residual carbon and nitrogen contents ofrespectively 2.8-2.9% and 1.0-1.1% for both untreated (RT-235) andtreated (DOW 550 coated RT-235) supported catalysts, even aftercalcination at 275° C. in air for 1 hour according to the procedure ofExample 3. Said carbon and nitrogen residue contents indicate theformation of organic remnants after partial decomposition of Ru-TEAcomplexes during said calcination step.

The results of Table 2 also show that the ruthenium dispersion on thetreated silica support (DOW 550 coated RT-235) was greatly increasedcompared to the untreated RT-235 silica support, with a H/Ruchemisorption ratio of 0.70 compared to 0.39. The hydroxyl groups of thesilica support are the anchoring points for the ruthenium. Without beingbound by any theory, it is believed that the higher Ru dispersion on thesilica surface, as shown by the higher H/Ru chemisorption ratio, resultsfrom a higher concentration of hydroxyl groups on the treated silicasupport, brought by the DOW 550 silica coating said higher Ru dispersionwill thus generate more active sites for phthalate hydrogenation.

The present invention has been described and illustrated by reference toparticular embodiments. Those of ordinary skill in the art willappreciate that the invention lends itself to variations not necessarilyillustrated herein. For this reason, then, reference should be madesolely to the appended claims for purposes of determining the true scopeof the present invention.

The invention claimed is:
 1. A method for the preparation of asilica-supported noble metal hydrogenation catalyst comprising the stepsof: (a) providing a silica support having a median pore size of at leastabout 10 nm; (b) steam treating said silica support to increase thehydroxyl concentration on the surface of said silica support afterstreaming to produce a steamed silica support; (c) contacting saidstreamed silica support with a silylating agent to coat at least part ofsaid streamed silica support to produce a coated silica support; (d)calcining said coated silica support obtained in step (c) to produce atreated and coated silica support; and (e) dispersing a noble metal by achelating agent on said treated and coated silica support obtained instep (d) to produce said silica-supported noble metal hydrogenationcatalyst having a median pore size of at least 10 nm and no more than300 nm.
 2. The method of claim 1, wherein said noble metal is selectedfrom the group consisting of ruthenium, rhodium, palladium, platinum,and mixtures thereof.
 3. The method of claim 2, wherein said noble metalis ruthenium.
 4. The method of claim 1, wherein said chelating agent hasfrom 2 to 20 carbon atoms and comprising at least one carboxylic acid orhydroxyl functional group and at least one nitrogen-containingfunctional group, wherein said nitrogen-containing functional group isan amine or an imine.
 5. The method of claim 1, wherein said chelatingagent is triethanolamine.
 6. The method of claim 1, wherein the methodfurther comprises the step (f) of calcining said silica-supported noblemetal hydrogenation catalyst produced in step (e) to produce a calcined,silica-supported noble metal hydrogenation catalyst.
 7. The method ofclaim 1, wherein said silica support used in step (a) has a median poresize of at least about 20 nm.
 8. The method of claim 1, wherein saidsilylating agent used in step (c) is a polysiloxane.
 9. The method ofclaim 1, wherein said silylating agent used in step (c) is apoly(alkylaryl) siloxane.
 10. The method of claim 1, wherein the surfacearea of said silica support, as measured by the BET method, isincreased, after steps (b) thru (e), by at least about 20 m²/g comparedto said surface area of said silica support used in step (a).
 11. Themethod of claim 1, wherein said hydroxyl group concentration of thetreated and coated silica support obtained in step (d) is increased byat least 1 Si—OH group per nm² as compared to that of the silica supportused in step (a).
 12. The method of claim 1, wherein saidsilica-supported noble metal hydrogenation catalyst has a hydrogen tonoble metal chemisorption ratio of at least about 0.50.
 13. The methodof claim 1, wherein said silica support used in step (a) has a crushstrength of at least 800 g/mm.
 14. The method of claim 1, furthercomprising the step of activating said silica-supported noble metalhydrogenation catalyst produced in step (e) by contacting said catalystwith hydrogen gas.
 15. The method of claim 6, further comprising thestep of activating said calcined, silica-supported noble metalhydrogenation catalyst produced in step (f) by contacting said catalystwith hydrogen gas.